Ronaldo was Ferdinand's team-mate at Manchester United for six years so the former defender knows the Portuguese better than most.
The 32-year-old has led Real Madrid to two Champions League wins in the last four years and helped them finally win the La Liga title back from Messi's Barcelona this season.
Ronaldo and Messi are often compared but Ferdinand believes they are both out on their own as the best there has been.
"To sustain this level of consistency and greatness for so long requires a dedication, a desire, sacrifice and this guy has got the determination to be the best all the time," he said on BT Sport.
Cristiano Ronaldo or Lionel Messi? Real Madrid and Barcelona fans debate who is better Wed, May 3, 2017
Cristiano Ronaldo equalled Lionel Messi's Champions League hat-trick record against Atletico Madrid, and fans still can't decide who is the more accomplished footballer
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Fans get heated once more over who is better – Cristiano Ronaldo or Lionel Messi
Rio Ferdinand says Cristiano Ronaldo and Lionel Messi are the two best players of all time
Cristiano Ronaldo and Lionel Messi stand out alone for me as the best players ever to play the game
Rio Ferdinand on Cristiano Ronaldo and Lionel Messi
"Whether it's in training, whether he's playing table tennis, whether he's being the best in terms of nutrition.
"This guy is an obsessed footballer who just wants to do what no other people are doing.
"Him and Messi stand out alone for me as the best players ever to play the game.
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"We can talk about the Diego Maradonas and the other great players, Ronaldinhos etc over the years and people will debate that.
Rio Ferdinand and Steven Gerrard were full of praise for Real Madrid star Cristiano Ronaldo
"But the consistency that these guys are operating at I think separates them."
"He's the perfect footballer, look at his physique," he said.
"He's also become a leader as well as the perfect footballer."